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A 200/1 Current Transformer (CT) is wound with 400 turns on the secondary on a toroidal core. When it carries a current of 180 A on the primary, the ratio is found to be -0.5%. If the number of secondary turns is reduced by 1, the new ratio error (in %) will be?(a) 0.0(b) -0.5(c) -1.0(d) -2.0I got this question in an online interview.This interesting question is from Problems Involving Coupling Coefficient topic in division Resonance & Magnetically Coupled Circuit of Network Theory

Answer»

Right answer is (C) -1.0

To explain I would SAY: Turn compensation only alters RATIO error n=400

Ratio error = -0.5% = – \(\frac{0.5}{100}\) × 400 = -2

So, Actual ratio = R = n+1 = 401

Nominal Ratio KN = \(\frac{400}{1}\) = 400

Now, if the number of turns are reduced by one, n = 399, R = 400

Ratio error = \(\frac{K_N-R}{R} = \frac{200-200}{200}\) = 0.



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